This invention relates to an FM receiver comprising an RF section, a first mixer stage for converting a desired RF reception signal to a first IF signal having a carrier frequency located on average at a first intermediate frequency, a first IF section for selecting the first IF signal, a second mixer stage for converting the first IF signal to a second IF signal having a carrier frequency located on average at a second intermediate frequency, said second intermediate frequency being below the first intermediate frequency, a second IF section for selecting the second IF signal, said second IF section being coupled to an FM demodulator for demodulating the baseband modulation signal of said desired RF reception signal, and followed by a low-pass filter for selecting the baseband modulation signal. The invention also relates to an IF stage for use in such an FM reciever.
An FM receiver of this type is known per se, for example, from the international PCT Patent Application WO 88/08223.
In the known FM receiver the first mixer stage is tunable and is used to convert a desired RF reception signal from an RF FM reception range down in frequency to a fixed first intermediate frequency of 10.7 MHz. The first 10.7 MHz IF signal thus obtained is selected in the first IF section and subsequently converted down in frequency again by means of the second mixer stage to a fixed second intermediate frequency of 700 kHz, resulting in said second IF signal. This second 700 kHz IF signal is demodulated by means of said FM demodulator after filtering.
In the frequency demodulation, signal multiplications and non-linear signal processing operations are performed so that mixing products and notably higher order interference components cannot be avoided. For an effective suppression of such interference components, complex and hence costly filters are required. Such filters impede the integration of the FM receiver.